Briggs wont turn over Cranks,has Spark, New Carb, Fuel pump works

[cgj212]

I have a briggs and stratton 12.5HP MN: 286707-4520-E1 cranks fasts,pops wont turn over. I've replaced the carb,spark plug theres spark found out hard way gapped to .03. Battery checks out 12v with multi meter, fuel pumps pumping gas. Engine just spins and spins wont start up.(also) all safety are off seat is bypassed tied together.

Any help would be greatly appreciated.


Thank you,
Chris G

 

[bertsmobile1]

Sounds like a blown head gasket.
Start by removing the rocker cover and see if the valves are opening & closing.

 

[mechanic mark]

https://www.briggsandstratton.com/e...ualSearch.html?searchrequested=286707-4520-e1

see page 6 in operators manual for tune up specs., you may need to adjust valves, intake .005-.007 & exhaust .009-.011.

https://www.google.com/search?q=how...ome..69i57.43119j0j4&sourceid=chrome&ie=UTF-8

https://www.youtube.com/watch?v=ot9yx09N_FI

 

[MowLife]

No rockers on this one being a flathead. Does sound like a compression issue though. Do you have good compression?

 

[cgj212]

No rockers on this one being a flathead. Does sound like a compression issue though. Do you have good compression?

I'm unsure at this point im going to buy a compression tool after work here. i'm unsure what range if should be in for good or bad though. and what to fix if it's bad

thank you for your response.

 

[cgj212]

Sounds like a blown head gasket.
Start by removing the rocker cover and see if the valves are opening & closing.

I'm going to buy a tool here tonight and check the compression.

Thank you for your time and response.

 

[cgj212]

Sorry i'm a newby here. I thank you all for your input i'll do your suggested compression test tonight and get back to you guys with the number later on.


Very Appreciated! :smile:

 

[MowLife]

I’ve had them old flatheads running with only 60lb compression. Hard to get a true reading with decompression mechanisms on the small motors. On your original post saying it spins fast on cranking has me wondering if there is compression loss. Could be a head gasket as stated earlier or a valve not sealing correctly. A leak down test is actually the best to pin point a leak. Most auto stores with loaner tools have these and normally is free.

 

[cgj212]

I'll have to look into a leak down test then. i wont even pretend to be any-kind of expert on this subject. leak down test is a new phrase for me. ill see what i can find on that.


thank you very much for the responses.

 

[MowLife]

It’s a very simple test but you do need a air compressor for the test. You basically put the piston at top dead center on compression stroke...this will have valves closed. Remove spark plug and insert the leak down test adapter in its place. Compressed air from the compressor fills combustion’s chamber and you listen for leaks. Noise from carb is intake valve leaking, noise from muffler is exhaust valve leaking, noise from oil fill tube is blow by or a head gasket blown. You normally hear a little noise in the filler tube but you don’t want much. I know this sounds confusing but to get an idea of how it works go to YouTube and search “Briggs leak down test” and there are examples. BTW you don’t need a big air compressor for this...I little tiny one works fine. There are ways to properly test using the gauges on the tester....but for small engines I just listen for air.